This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
A milestone was recently reached for multimedia broadcast/multicast service (MBMS) in that there has been a large scale commercial deployment of streaming mobile television by a large wireless carrier, specifically using the MediaFLO® model. MBMS in general is a point to multipoint service which is able to securely transmit data, like Mobile TV, to a given set of users that subscribed to the service. The security works as such that there are user specific keys, which like the service keys are handled in a point-to-point manner, while the service content related keys are multicast/broadcast based. Further details as to MBMS security (eMBMS for the evolved UTRAN or LTE systems) may be seen in the technical specification 3GPP TS 33.246 v10.0.0. To cover a wide geographical area carriers typically need to deploy more than one broadcasting server, depending on how many delivery points each server supports. The end user may move between the coverage of those servers from which end users receive the MBMS stream, such as when users travel to and from work.
The security architecture for MBMS is based on a generic bootstrapping architecture (GBA), but GBA was not designed for mobility between MBMS servers (named BM-SCs). Specifically, the key hierarchy in MBMS has two classes of keys as can be seen in the prior art table at FIG. 1: user-specific and service-specific. FIG. 1A illustrates four security keys:                MTK (MBMS traffic key) is used to encrypt MBMS data (e.g. Mobile TV data) in the BMSC or backend server and to decrypt data in the user equipment (UE) also called terminal;        MSK (MBMS service key) is generated by the BMSC and is used to decrypt the service specific MTKs;        MUK (MBMS user key) is used to encrypt the MSKs in the BMSC before they are send to the UEs and used by the terminal to decrypt; and        MRK (MBMS request key) is used by the BMSCs to authenticate and authorize a terminal MSK request.The MUK and the MRK are user specific and server specific (i.e. bound to a specific BMSC based on GBA), while the MSK and MTK are service specific.        
As shown at FIG. 1B, the OMA Broadcast BCAST system has the same logical key hierarchy, with TEK as the traffic key, SEK and PEK as the service key, SMK and REK similar to the user key, and SI (shared or private) similar to the user authentication/request key. OMA Broadcast also suffers similar deficiencies with regard to the combination of mobility and security. The teachings below explain some security issues that arise when using GBA for mobile streaming with mobility between servers, and how to address those security issues.
The invention applies to any device or terminal that is able to generate GBA-based cryptographic keys and are able to receive MBMS or BCAST messages, i.e. not necessarily only mobile phones.